Exercise and health

• Strong correlations between obesity and lack of exercise

• ALSO a causal mechanism; lack of exercise means it's harder to burn off the energy taken in as food

Occurs either because

• you can't make enough insulin for your needs
• your body cells no longer respond to the insulin you make

Increasing exercise levels leading to weight loss can prevent type 2 diabetes - clear correlation

Moderate exercise is linked to a reduced number of colds

Some scientific data links heavy athletic training with an increase in minor infections. This is not necessarily causative, but may be because:

• the immune system is suppressed after extreme exertion
• large number of people from diverse areas are in close proximity during sporting events, so viruses spread easily
• athletes often travel to sporting events by air, which exposes them to pathogens

Causal investigations into how the immune system responds to exercise

• Moderate exercise increases number of T killer cells
• Very intensive exercise reduces the numbers and activity of T killer cells
• Very intensive exercise may also reduce phagocytes, B cells and T helper cells
• Competition and intense exercise releases stress hormones like cortisol and adrenaline. These suppress inflammation and reduce antibody production

Unclear whether it is the level of exercise or stress that causes any adverse effect on the immune system following intensive exercise